Quartz Monzodiorite Research Articles

High-K, calc-alkaline I-type granitoids from the composite Yozgat batholith generated in a post-collisional setting following continent-oceanic island arc collision in central Anatolia, Turkey

The composite Yozgat batholith consists of a S-I-A-type granitoid association intruding the supra-subduction zone-type (SSZ-type) central Anatolian ophiolite and medium- to high-grade metasedimentary rocks of the central Anatolian crystalline complex. These rocks are unconformably covered by Palaeocene to Early Eocene sedimentary rocks. The I-type granitoids are the most common rock association of this huge batholith. In an area between the towns of Şefaatli and Yerkoy, the southwestern part of the batholith can be subdivided into five mappable units: the Akcakoyunlu quartz monzodiorite (mafic; hornblende K-Ar cooling ages of 77.6–79.3 Ma); the Cankili monzodiorite (mafic; hornblende K-Ar cooling age of 71.1 Ma); the Adatepe quartz monzonite (mafic; hornblende K-Ar cooling age of 68.0 Ma); the Yassiagil monzogranite (felsic; hornblende + biotite K-Ar cooling ages of 69.9–79.8 Ma) and the Karakaya monzogranite (felsic; hornblende + biotite K-Ar cooling ages of 71.3–77.0 Ma). All the lithological units, except the Karakaya monzogranite, include large K-feldspar megacrysts and various types of mafic microgranular enclaves in field outcrops, indicating mingling and mixing. In addition, microscopic textures showing the hybridization between the coeval mafic and felsic magma sources are present. Whole-rock major element geochemistry shows a high-K calc-alkaline, metaluminous, I-type composition with an aluminium saturation index (ASI) less than 1.10 and with CIPW diopside content in all the lithological units. Large ion lithophile elements (LILE), light rare earth elements (LREE), some high field strength elements (HFSE) (except Nb) enrichments and significant crustal contribution revealed by the oxygen and sulphur stable isotope compositions in the mafic and felsic I-type granitoid units are consistent with mafic lower crustal and metasomatized mantle sources the latter of which were metasomatized by earlier supra subduction zone (SSZ)-derived fluids during the development of the SSZ-type central Anatolian ophiolite.

Fluid Evolution in the Formation of the Fenghuangshan Cu-Fe-Au Deposit, Tongling, Anhui, China

The Fenghuangshan Cu-Fe-Au deposit is located in Tongling, Anhui province in central-east China, within the Middle-Lower Yangtze River polymetallic belt. The mineralization is related to Late Yanshanian magmatic intrusions emplaced in Lower Triassic limestones and is divided into two episodes. The first and more important, episode A, is related to granodiorite-granodiorite porphyry and characterized by massive, disseminated, veinlet- and breccia-style mineralization in skarn formed at the contact zone, whereas the second, episode B, is related to a quartz monzodiorite porphyry stock which crosscuts the previous skarn and is characterized by disseminated and veinlet-style mineralization within the porphyry. Based on mineral assemblages and their crosscutting relationships, the hydrothermal evolution of episode A is further divided into five substages (A1–A5), and that of episode B into four (B1–B4), among which A4, A5, and B3 are the main copper mineralization stages. This paper focuses on microthermometric studies of fluid inclusions in the various stages, with an aim to characterize the thermal and compositional evolution of hydrothermal fluids and to discuss their implications for mineralization in terms of fluid sources and metal deposition mechanisms. Fluid inclusions were studied in garnet, quartz, and calcite from stages A1, A4, A5, B1, B2, B3, and B4. Four types and 13 subtypes of fluid inclusions were distinguished based on fluid composition and phase assemblages. Type I fluid inclusions contain one or more salt daughter minerals (halite and sylvite) and homogenize into the liquid phase, whereas type II inclusions homogenize into the vapor phase, both commonly containing an opaque daughter mineral. Type III fluid inclusions are aqueous inclusions that do not contain daughter minerals and homogenize into the liquid phase, and type IV inclusions are CO2 bearing, homogenize to the CO2 or the aqueous phase, and commonly contain an opaque daughter mineral. Primary fluid inclusions in stage A1 are of type I and II, interpreted to represent two immiscible phases resulting from boiling, and those in stages A4 and A5 are of type III. Stages B1 and B2 are characterized by type I primary inclusions, and stages B3 and B4 by type III. Type IV inclusions occur as secondary inclusions in B1 quartz and are interpreted to be related locally to B3 stage mineralization. Microthermometric data indicate a trend of decreasing temperatures and salinities from early to late stages for both mineralization episodes, reflecting a change from a magmatic fluid-dominated system to one invaded by fluids from the country rocks and meteoric water. The fact that the main stages of mineralization (A4, A5, B3) coincided with the development of fluid inclusions without daughter minerals of salt suggests that sulfide precipitation did not take place until the system was diluted by cooler fluids with lower salinities. However, the observation that the fluid inclusions hosted in minerals before sulfide mineralization (i.e., stages A1, B1, and B2) commonly contain opaque daughter minerals inferred to be sulfides suggests that the ore-forming components were likely derived from the higher temperature magmatic fluids, and the fluids derived from the country rocks mainly contributed to the precipitation of sulfides through mixing and cooling.

Evidence for a pulse of 1.45 Ga anorthosite–mangerite–charnockite–granite (AMCG) plutonism in Lithuania: implications for the Mesoproterozoic evolution of the East European Craton

AbstractSeveral subcropping anorthosite–mangerite–charnockite–granite (AMCG) plutonic suites are aligned along E–W trending lineaments in the Lithuanian part of the East European Craton. The Rukai quartz monzodiorite from the Nemunas suite yields a zircon U–Pb intrusion age of 1447 ± 5 Ma, and the Geluva granite an age of 1445 ± 8 Ma, both obtained using secondary ion mass spectrometry. These rocks are 50 Myr younger than the 1.53–1.50 Ga Mazury AMCG complex in southern Lithuania and northern Poland.The Nemunas and Geluva AMCG rocks correlate in age with Bornholm granitoids in the Baltic Sea and Blekinge granites in southern Sweden, and are similarly aligned along E–W trending lineaments. This regional 1.45 Ga magmatic event across the Baltic Sea may be regarded as an inboard manifestation of the accretionary 1.50 Ga Danopolonian orogeny (cf. Pol. Mineral. Soc. Spec. Publ., 2005, 26:18) farther west.

Petrochemistry and petrology of I-type granitoids in an arc setting: the composite Torul pluton, Eastern Pontides, NE Turkey

The Upper Cretaceous Torul pluton, located in the Eastern Pontides, is of sub-alkaline affinity and displays features typical of volcanic arc granitoids. It is a composite pluton consisting of granodiorite, biotite hornblende monzogranite, quartz monzodiorite, quartz monzonite and hornblende biotite monzogranite. The oldest syenogranite (77.9 ± 0.3 Ma) and the youngest quartz diorite form small stocks within the pluton. Samples from the granodiorites, biotite hornblende monzogranites, quartz monzodiorites, quartz monzonites and hornblende biotite monzogranites have SiO2 between 57 and 68 wt% and display high-K calc-alkaline, metaluminous to peraluminous characteristics. Chondrite-normalized REE patterns are fractionated (Lacn/Lucn = 6.0−14.2) with pronounced negative Eu anomalies (Eu/Eu* = 0.59–0.84). Initial ɛNd(i) values vary between −3.1 and −4.1, initial 87Sr/86Sr values between 0.7058 and 0.7072, and δ18O values between +4.4 and +7.3‰. The quartz diorites are characterized by relatively high Mg-number of 36–38, low contents of Na2O (2.3–2.5 wt%) and SiO2 (52–55 wt%) and medium-K calc-alkaline, metaluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)cn = 2.8–3.3; (Tb/Yb)cn = 1.2] and show small negative Eu anomalies (Eu/Eu* = 0.74–0.76). Compared to the other rock types, radiogenic isotope signatures of the quartz diorites show higher 87Sr/86Sr (0.7075–0.7079) and lower ɛNd(i) (–4.5 to –5.3). The syenogranites have high SiO2 (70–74 wt%) and display high-K calc-alkaline, peraluminous characteristics. Their REE patterns are characterized by higher Lacn/Lucn (12.9) and Eu/Eu* (0.76–0.77) values compared to the quartz diorites. Isotopic signatures of these rocks [ɛNd(i) = −4.0 to −3.3; 87Sr/86Sr(i) = 0.7034−0.7060; δ18 O = + 4.9 to + 8.2] are largely similar to the other rock types but differ from that of the quartz diorites. Fractionation of plagioclase, hornblende, pyroxene and Fe–Ti oxides played an important role in the evolution of Torul granitoids. The crystallization temperatures of the melts ranged from 800 to 900°C as determined from zircon and apatite saturation thermometry. All these characteristics, combined with low K2O/Na2O, low Al2O3/(FeOT + MgO + TiO2), and low (Na2O + K2O)/(FeOT + MgO + TiO2) ratios suggest an origin through dehydration melting of mafic lower crustal source rocks.

Copper-gold endoskarns and high-Mg monzodiorite–tonalite intrusions at Mt. Shea, Kalgoorlie, Australia: implications for the origin of gold–pyrite–tennantite mineralization in the Golden Mile

Five Cu–Au epidote skarns are associated with the Mt. Shea intrusive complex, located in the 2.7–2.6 Ga Eastern Goldfields Province of the Archean Yilgarn craton, in greenstones bounded by the Boulder Lefroy and Golden Mile strike-slip faults, which control the Golden Mile (1,435 t Au) at Kalgoorlie and smaller “orogenic” gold deposits at Kambalda. The Cu–Au deposits studied are oxidized endoskarns replacing faulted and fractured quartz monzodiorite–granodiorite. The orebodies are up to 140 m long and 40 m thick. Typical grades are 0.5% Cu and 0.3 g/t Au although parts are richer in gold (1.5–4.5 g/t). At the Hannan South mine, the skarns consist of epidote, calcite, chlorite, magnetite (5–15%), and minor quartz, muscovite, and microcline. Gangue and magnetite are in equilibrium contact with pyrite and chalcopyrite. The As–Co–Ni-bearing pyrite contains inclusions of hematite, gold, and electrum and is intergrown with cobaltite and Cu–Pb–Bi sulfides. At the Shea prospect, massive, net-textured, and breccia skarns are composed of multistage epidote, actinolite, albite, magnetite (5%), and minor biotite, calcite, and quartz. Gangue and magnetite are in equilibrium with Co–Ni pyrite and chalcopyrite. Mineral-pair thermometry, mass-balance calculations, and stable-isotope data (pyrite δ34SCDT = 2.5‰, calcite δ13CPDB = −5.3‰, and δ18OSMOW = 12.9‰) indicate that the Cu–Au skarns formed at 500 ± 50°C by intense Ca–Fe–CO2–S metasomatism from fluids marked by an igneous isotope signature. The Mt. Shea stock–dike–sill complex postdates the regional D1 folding and metamorphism and the main phase of D2 strike-slip faulting. The suite is calc-akaline and comprises hornblende–plagioclase monzodiorite, quartz monzodiorite, granodiorite, and quartz–plagioclase tonalite porphyry. The intrusions display a wide range in silica content (53–73 wt% SiO2), in $$ {{\text{Mg}}} \mathord{\left/ {\vphantom {{{\text{Mg}}} {{\left( {{\text{Mg}} + {\text{Fe}}_{{{\text{TOTAL}}}} } \right)}}}} \right. \kern-\nulldelimiterspace} {{\left( {{\text{Mg}} + {\text{Fe}}_{{{\text{TOTAL}}}} } \right)}} $$ ratio (0.37–0.89), and in $$ {\text{K}} \mathord{\left/ {\vphantom {{\text{K}} {{\left( {{\text{K}} + {\text{Na}}} \right)}}}} \right. \kern-\nulldelimiterspace} {{\left( {{\text{K}} + {\text{Na}}} \right)}} $$ ratio (0.02–0.31). Chromium (62–345 ppm), Ni (23–158), Sr (311–1361 ppm), and Ba (250–2,581 ppm) contents are high, Sr/Y ratios are high (24–278, mostly >50), and the rare earth element patterns are fractionated $$ {\left( {{{\text{Ce}}_{N} } \mathord{\left/ {\vphantom {{{\text{Ce}}_{N} } {{\text{Yb}}_{N} = 17 - 41}}} \right. \kern-\nulldelimiterspace} {{\text{Yb}}_{N} = 17 - 41}} \right)} $$ . These features and a negative niobium anomaly relative to the normal mid-ocean ridge basalt indicate that the suite formed by hornblende fractionation from a subduction-related monzodiorite magma sourced from metasomatized peridotite in the upper mantle. The magnesian composition of many intrusions was enhanced due to hornblende crystallization under oxidizing hydrous conditions and during the subsequent destruction of igneous magnetite by subsolidus actinolite–albite alteration. At the Shea prospect, main-stage Cu–Au epidote skarn is cut by biotite–albite–dolomite schist and by red biotite–albite replacement bands. Post-skarn alteration includes 20-m-thick zones of sericite–chlorite–ankerite schist confined to two D3 reverse faults. The schists are mineralized with magnetite + pyrite + chalcopyrite (up to 0.62% Cu, 1.6 g/t Au) and are linked to skarn formation by shared Ca–Fe–CO2 metasomatism. Red sericitic alteration, marked by magnetite + hematite + pyrite, occurs in fractured porphyry. The biotite/sericite alteration and oxidized ore assemblages at the Shea prospect are mineralogically identical to magnetite–hematite-bearing gold lodes at Kambalda and in the Golden Mile. Published fluid inclusion data suggest that a “high-pressure”, oxidized magmatic fluid (2–9 wt% NaCl equivalent, $$ X_{{{\text{CO}}_{2} }} = 0.1 - 0.2 $$ , 200–400 MPa) was responsible for gold mineralization in structural sites of the Boulder Lefroy and Golden Mile faults. The sericite–alkerite lodes in the Golden Mile share the assemblages pyrite + tennantite + chalcopyrite and bornite + pyrite, and accessory high-sulfidation enargite with late-stage sericitic alteration zones developed above porphyry copper deposits.

Porphyry Cu-Mo-(Au) mineralization: the age and relationship with igneous rock complexes of the Borgulikan ore field (upper-Amur region)

The Borgulikan ore field is localized in the west of the Umlekan-Ogodzha volcanoplutonic belt made up of various igneous (upper-Amur granite-granodiorite (140–134 Ma), Burunda monzodiorite-granodiorite (130–127 Ma), and Taldan andesite (127–123 Ma)) and superposed (Early Cretaceous Gal’ka trachybasalt-rhyolite (119–115 Ma) and Late Cretaceous trachybasalt-trachyandesite (97–94 Ma)) complexes. 40Ar/ 39Ar dating of porphyry intrusions breaking through the Taldan volcanic complex and associated with Cu-Mo-(Au) mineralization yielded the following ages: early (dark) “pre-ore” quartz monzodiorite porphyrites — 125.8±0.7 Ma (groundmass) and 125.2±1.8 Ma (biotite phenocrysts); late (cream) “syn-ore” quartz monzodiorite porphyrites — 122.6±0.7 Ma (biotite phenocrysts). In age and many geochemical features the quartz monzodiorite porphyrites are close to the Taldan complex volcanics. Both of these rocks seem to belong to the same volcanoplutonic association.

40Ar/39Ar Geochronology of Alteration and Petrogenesis of Porphyry Copper-Related Granitoids in the Darreh-Zerreshk and Ali-Abad area, Central Iran

Darreh-Zerreshk and Ali-Abad are two relatively small porphyry copper-type deposits in Yazd Province in central Iran. They are located within the central Iranian volcano-plutonic belt, formed above the collisional convergent margin of the Iranian lithospheric plate from the late Eocene to the Miocene. This paper discusses the geochemical characteristics of the igneous rocks, and 40 Ar/ 39 Ar geochronology of plutons and alteration phases associated with the Darreh-Zerreshk and Ali-Abad deposits. The deposits are spatially associated with igneous complexes that consist of older and barren granites intruded by intermediate-composition granitoids, which are the carriers of Cu mineralization. The granites have relatively high content of Nb, Y, and K, a prominent negative Eu anomaly, and were probably derived from melting of, or contamination of mantle-derived magmas by, continental crust. Porphyritic diorites, quartz monzodiorites, and granodiorites show enrichment in light rare earth and large-ion lithophile elements, depletion in middle rare earth elements, and have no negative Eu anomaly. These intermediate-composition granitoids were derived from melting of the upper mantle or lower crust, and their differentiation was controlled partly by fractionation of hornblende. A pilot K/Ar whole-rock dating study suggests that the pre-ore granites were emplaced in the Oligocene. Dating by the 40 Ar/ 39 Ar method of nine samples of secondary biotite and sericitized rocks from drillcore within the mineralized and altered zones in both deposits yielded a well-defined age of ca. 16 Ma. This date is interpreted to be the time of hydrothermal alteration and of porphyry copper type mineralization in this part of Iran.

Age, petrology and geochemistry of the porphyritic Aitik intrusion, and its relation to the disseminated Aitik Cu-Au-Ag deposit, northern Sweden

The Aitik Cu-Au-Ag deposit in northern Sweden is hosted by strongly altered and deformed 1.9 Ga old Svecofennian volcaniclastic rocks. A porphyritic quartz monzodiorite intrusion of subvolcanic origin is situated in the structural footwall to the ore. U–Pb TIMS zircon dating of the quartz monzodiorite yielded an age of 1887±8 Ma, which coincides with the age obtained for the subduction-related Haparanda suite of granitoids in Norrbotten. It is intruded by minor, comagmatic phases, including units of finer grained quartz monzodiorite and diorite. The finer grained intrusive phase, which can be traced into the ore zone of the Aitik deposit, is believed to represent apophyses protruding from the upper part of the quartz monzodiorite. The Aitik intrusion, comprising the quartz monzodiorite and its comagmatic phases, is affected by regional metamorphism, deformation, and hydrothermal alteration. Potassic alteration is most evident, and expressed by the growth of secondary biotite and K-feldspar. The sub-economic Cu-Au-Ag mineralization hosted by the Aitik intrusion mainly consists of chalcopyrite, pyrite, and magnetite of dominantly magmatic-hydrothermal origin, and is present in four forms: disseminated, as veinlets, in quartz-feldspar veins, and in biotite-amphibole veins. This mineralization extends in economic grades into the adjacent volcaniclastic rocks in the roof of the intrusion. The Aitik intrusion is similar in many respects to porphyry copper generating intrusions regarding tectonic setting, petrography and chemical composition. The intrusion-hosted sub-economic mineralization might form part of a porphyry system with its major part represented by the main mineralization in the overlying volcaniclastic rocks.

The Žemaičių Naumiestis granitoids: New evidences for Mesoproterozoic magmatism in western Lithuania

We report new occurrences of ca. 1460 Ma magmatism in western Lithuania, where large volumes of granitoid melts were intruded into host supracrustal and charnockitoid rocks, and formed the Žemaičių Naumiestis pluton. Numerous granitoids of that age have previously been described from southern Sweden and from the Danish island of Bornholm, but none have been reported from the eastern side of the Baltic Sea, where the crystalline basement is covered by Phanerozoic sediments. Petrological studies demonstrate that the Žemaičių Naumiestis intrusion consists of quartz monzodiorites, monzogranites and syenogranites. The dominant ferromagnesian mineral is biotite. Rare clinopyroxene grains occur in the quartz monzodiorites. The rocks are fine to coarse-grained, often porphyritic. Chemically, the studied granitoids are dominantly alkali-calcic and shoshonitic, metaluminous to peraluminous, and ferroan to magnesian. The geochemical data indicate that the pluton consists of two rock suites, one representing monzodiorites and monzogranites, and other mostly syenogranites. The suites originated from slightly different sources. The rocks within the Žemaičių Naumiestis pluton are variably deformed and locally cataclased. Some are, however, rather massive. Two samples of monzogranite yielded ID-TIMS U-Pb zircon ages of 1462±8 (MSWD = 1.09) and 1459±3 Ma (MSWD = 0.28).

Granitic Magmatism in the North Qaidam Early Paleozoic Ultrahigh-Pressure Metamorphic Belt, Northwest China

Three suites of granitic rocks are present in the early Paleozoic North Qaidam ultrahigh-pressure (UHP) metamorphic belt, which has eclogite ages of 466-495 Ma. The first suite consists of quartz monzodiorite + granodiorite + monzogranite, the second of monzogranite + two-mica granite + muscovite granite + syenogranite, and the third of granodiorite + monzogranite + biotite granite. The country rocks into which these bodies were intruded consist chiefly of medium- and high-grade Proterozoic gneisses and schists and Paleozoic sedimentary and volcanic rocks. Monzogranite of the first suite has a zircon SHRIMP age of 473 Ma, whereas syenogranite in the second suite has an age of 446 Ma, and granodiorite in the third suite has an age of 397 Ma. Rocks of the first and third suites have similar mineralogies consisting of plagioclase, hornblende, quartz, alkali feldspar, and biotite, whereas those of the second suite consist of potassium feldspar, quartz, muscovite, biotite, and plagioclase. Rocks of the first and third suites have I-type compositions with SiO2 = 61-69 wt%, Na2O/K2O >1, ANK <1, and Eu/Eu* = 0.7-1.0, whereas the second suite consists of S-type granites, with SiO2 = 70-76 wt%, Na2O/K2O <1, ANK >1, and Eu/Eu* = 0.1-0.3. The first suite is interpreted as island arc or active continental margin magmatism, the second as igneous activity related to collision between the Qaidam and Qilian blocks, and the third as post-collisional plutonic activity.

Porosity in crystalline rocks – A matter of scale

The pore space (porosity) in a crystalline rock is the sum of microfractures, intragranular pores and fluid inclusions. The total porosity can be divided into connected (characterized by flow and diffusion) and unconnected porosity (due to isolated pores). The different porosities are distinguished by different methods of measurement but are dependent on sample size and shape. The present study presents porosity measurements carried out on samples from a drill-core from the porphyritic Äspö quartz monzodiorite, SE Sweden. Water saturation measured on eleven 60-mm-long core pieces has been used to calculate the connected porosity. This ranges between 0.32 and 0.44 vol.%. Some of the 60-mm samples were subsequently cut into 35 slices of various thicknesses (3 mm, 6 mm, 10 mm and 20 mm), and water saturation was measured on all these. On average, higher connected porosity values were measured in the thin slices compared with the 60-mm-thick samples. This is mainly because the thinner samples have a higher relative portion of pores created by mechanical failure than the thicker samples; this is also due to a higher portion of microfractures which have lengths exceeding the thicknesses of the samples. However, the variation is much larger for the thin sample (values between 0.45 and 0.68 vol.% were measured for the 3-mm slices). This larger variation is also valid for the density measurements indicating less relative homogeneity in the thin slices. Eleven of the samples were ground to powder in order to measure grain densities and bulk and grain densities were used to calculate total porosity. The total porosity varied from 0.9 to 1.5 vol.% (∼70% between 0.98 and 1.23 vol.%). The portion of connected pores in relation to total porosity amounts to 33–60% of which the lower values represent 60-mm-thick samples. Most microfractures are orientated along the foliation and are mostly related to K-feldspar and quartz grains.

Geology and Reconnaissance Stable Isotope Study of the Oyu Tolgoi Porphyry Cu-Au System, South Gobi, Mongolia

The Oyu Tolgoi porphyry Cu-Au system in the South Gobi desert, Mongolia, comprises five deposits that extend over 6 km in a north-northeast‐oriented zone. They occur in a middle to late Paleozoic arc terrane and are related to Late Devonian quartz monzodiorite intrusions. The Hugo Dummett deposits are the northernmost and deepest, with up to 1,000 m of premineral sedimentary and volcanic cover rock remaining. They are the largest deposits discovered to date and characterized by high-grade copper (>2.5% Cu) and gold (0.5‐2 g/t) mineralization associated with intense quartz veining and several phases of quartz monzodiorite intruded into basaltic volcanic host rocks. Sulfide minerals in these deposits are zoned outward from a bornite-dominated core to chalcopyrite, upward to pyrite ± enargite and covellite at shallower depth. The latter high-sulfidation‐state sulfides are hosted by advanced argillic alteration mineral associations. This alteration is restricted mainly to dacitic ash-flow tuff that overlies the basaltic volcanic rock and includes ubiquitous quartz and pyrophyllite, kaolinite, plus late dickite veins, as well as K alunite, Al phosphate-sulfate minerals, zunyite, diaspore, topaz, corundum, and andalusite. A reconnaissance oxygen-hydrogen and sulfur isotope study was undertaken to investigate the origin of several characteristic alteration minerals in the Oyu Tolgoi system, with particular emphasis on the Hugo Dummett deposits. Based on the isotopic composition of O, H, and S (δ18O(SO4) = 8.8‐20.1‰, δD = ‐73 to ‐43‰, δ34S = 9.8‐17.9‰), the alunite formed from condensation of magmatic vapor that ascended to the upper parts of the porphyry hydrothermal system, without involvement of significant amounts of meteoric water. The isotopic data indicate that pyrophyllite (δ18O = 6.5‐10.9‰, δD = ‐90 to ‐106‰) formed from a magmatic fluid with a component of meteoric water. Muscovite associated with quartz monzodiorite intrusions occurs in the core of the Hugo Dummett deposits, and isotopic data (δ18O = 3.0‐9.0‰, δD = ‐101 to ‐116‰) show it formed from a magmatic fluid with water similar in composition to that which formed the pyrophyllite. Mg chlorite (δ18O = 5.5‰, δD = ‐126‰) is a widespread mineral retrograde after hydrothermal biotite and may have formed from fluids similar to those related to the muscovite during cooling of the porphyry system. By contrast, paragenetically later and postmineralization alteration fluid, which produced dickite (δ18O = ‐4.1 to +3.3‰, δD = ‐130 to ‐140‰), shows clear evidence for mixing with substantial amounts of meteoric water. Relatively low δD values (‐140‰) for this meteoric water component may indicate that its source was at high elevations. The geologic structure, nature of alteration, styles of mineralization, and stable isotope data indicate that the Oyu Tolgoi deposits constitute a typical porphyry system formed in an island-arc setting. The outward zonation of sulfide minerals for the Hugo Dummett deposits, from a bornite-dominated core to chalcopyrite and pyriteenargite, can be interpreted to be related to a cooling magmatic hydrothermal system which transgressed outward over enclosing advanced argillic alteration. This resulted in some unusual alteration and sulfide parageneses, such as topaz, or pyrite, enargite, and tennantite, entrained by high-grade bornite.

Timing of Magmatism following Initial Convergence at a Passive Margin, Southwestern U.S. Cordillera, and Ages of Lower Crustal Magma Sources

Initiation of the Cordilleran magmatic arc in the southwestern United States is marked by intrusion of granitic plutons, predominantly composed of alkali‐calcic Fe‐ and Sr‐enriched quartz monzodiorite and monzonite, that intruded Paleoproterozoic basement and its Paleozoic cratonal‐miogeoclinal cover. Three intrusive suites, recognized on the basis of differences in high field strength element and large ion lithophile element abundances, contain texturally complex but chronologically distinctive zircons. These zircons record heterogeneous but geochemically discrete mafic crustal magma sources, discrete Permo‐Triassic intrusion ages, and a prolonged postemplacement thermal history within the long‐lived Cordilleran arc, leading to episodic loss of radiogenic Pb. Distinctive lower crustal magma sources reflect lateral heterogeneity within the composite lithosphere of the Proterozoic craton. Limited interaction between derived magmas and middle and upper crustal rocks probably reflects the relatively cool thermal structure of the nascent Cordilleran continental margin magmatic arc.

Discovery of the Early Paleozoic post-collisional granites in northern margin of the Erguna massif and its geological significance

The Luoguhe intrusion, located in Mohe County, Heilongjiang Province, is mainly composed of monzogranite, quartz diorite and granodiorite, with minor diorite, tonalite, quartz monzodiorite, quartz monzonite, syenogranite and alkali-feldspar granite. The intrusion can be divided into two lithological units, i.e. quartz diorite and monzogranite units, with affinities to high-K calc-alkaline series. The quartz diorite unit (SiO2: 54.79%–58.30%, Na2O/CaO: 0.79–1.53 and Shand index: 0.77–0.82) belongs to metaluminous rocks. And the monzogranite unit (SiO2: 65.29%–66.45%, Na2O/CaO: 1.73–3.43 and Shand index < 1.05) can be considered as weakly peraluminous rocks. The intrusion is characterized by high REE abundance (ΣREE = 180.2-344.3 µg/g), medium-strong negative Eu anomalies (δEu = 0.33-0.82), weak REE fractionation [(La/Yb)N = 4.12-10.45], enrichments in Rb, Th, U, K, La, Ce, Nd, Hf, Zr and Sm, but strong depletions of Ba, Nb, Ta, Sr, P and Ti. These characteristics of major, REE and trace elements indicate that the intrusion was formed in a transitional tectonic setting from compressional to extensional regime, which can be classified as post-collisional granitoids. SHRIMP U-Pb zircon analyses yield ages of 517±9 and 504±8 Ma for the quartz diorite and monzogranite units, respectively. The discovery of Early Paleozoic post-collisional granites in the northern margin of the Erguna massif indicates that the northern branch of Paleo-Asian Ocean between Siberian plate and Erguna massif was closed in the Early Paleozoic and the Salair orogeny ended ca. 500 Ma ago.

SHRIMP U‐Pb Zircon Geochronology of the Xiaotongguanshan and Shatanjiao Intrusions and Its Petrological Implications in the Tongling Area, Anhui

Abstract This paper determines the crystallization ages of the Xiaotongguanshan quartz monzodiorite and Shatanjiao quartz monzonite porphyry from the Tongling area using the SHRIMP zircon U‐Pb method. The crystallization age of the former is 142.8±1.8 Ma; that of the latter is 151.8±2.6 Ma. These data indicate that they were formed during the Late Jurassic (142.8 to 151.8 Ma). Zoned magma chamber was formed because of double diffusive convection. Therefore, the intrusive sequence of magma is generally from quartz monzonite through quartz monzodiorite to pyroxene monzodiorite, i.e. an inverted sequence.

Ages of Intrusion, Alteration, and Mineralization at the Grasberg Cu-Au Deposit, Papua, Indonesia

The 40Ar/39Ar ages of 10 magmatic and hydrothermal micas from the Grasberg Igneous Complex range from 3.33 ± 0.12 to 3.01 ± 0.06 Ma. The ages of intrusive rocks and the paragenetic relationships between intrusive rocks and hydrothermal alteration and mineralization indicate that the Grasberg Igneous Complex formed during several cycles of intrusion and hydrothermal alteration. These include the Dalam and Main Grasberg intrusion and alteration cycles (3.33 ± 0.12–3.19 ± 0.05 Ma), a Kali intrusion and alteration cycle (3.16 ± 0.06–3.06 ± 0.03 Ma), and a post-Kali intrusion and Grasberg mineralization cycle (3.06 ± 0.03 and 3.01 ± 0.06 Ma). Each cycle of intrusion and alteration appears to have lasted around 0.1 m.y. or less and indicates that the huge size and high grade of Grasberg did not result from an unusually prolonged period of hydrothermal activity. A sample of phlogopite predating magnetite from the Kucing Liar Cu-Au deposit adjacent to Grasberg has an age of 3.41 ± 0.03 Ma. This is within error of the age of a Dalam intrusive rock from the Grasberg Igneous Complex and suggests formation of the calc-silicate skarn part of Kucing Liar at an early stage in the development of the complex. The ages of the equigranular diorite from the Ertsberg intrusion (2.67 ± 0.03 Ma), phlogopite from an endoskarn vein in the intrusion (2.71 ± 0.04 Ma), and phlogopite from the Ertsberg Cu-Au deposit (2.59 ± 0.15 Ma) indicate that intrusion and alteration and/or mineralization at Ertsberg are younger than the intrusions and mineralization in the Grasberg Igneous Complex. The Ertsberg therefore represents at least one additional cycle of approximately 0.1 m.y. of intrusion and alteration and/or mineralization in the district. The intrusions that make up the Grasberg Igneous Complex and Ertsberg and the hydrothermal fluids responsible for much of the alteration and mineralization appear to have been derived from a deeper level magma chamber. The youngest dated intrusive phase in the Grasberg Igneous Complex is a post-Kali diorite dike that is more basic than the preceding Kali quartz monzodiorite intrusions. This, together with the presence of mafic xenoliths in the Kali and Ertsberg intrusions, suggests that the magma chamber from which the intrusions and fluids were sourced was periodically replenished by basic magma. This process may also have triggered release of magma to form the shallow-level intrusions now exposed at the surface. The basic magmas also may have contributed components including fluids, metals, and/or sulfur to the Cu-Au deposits in the Ertsberg district.

Mineralogy, petrography and whole-rock geochemistry of the Tertiary granitic intrusions in the Eastern Pontides, Turkey

Granitic intrusions in Eocene and post-Eocene volcanic rocks outcrop in the Northern and Southern Zones of the Eastern Pontides, NE Turkey. Intrusions in the Northern Zone extend NW–SE whereas those in the Southern Zone are nearly E–W orientated. The contacts of the intrusions with the volcanic rocks are sharp, epidotized and include volcanic xenoliths. The margins of Southern Zone intrusions often contain abundant angular mafic microgranular enclaves of diorite to quartz diorite composition. The rocks also show evidence of mingling and mixing between coeval mafic and felsic magmas. Field observations suggest a stopping type of ascent and emplacement style for the intrusions. Petrographically, intrusions show variations in both colour and mineralogy with fine to medium granular, monzonitic, poikilitic, rapakivi, anti-rapakivi and graphic textures. Based on modal mineralogy, the Northern rocks are monzonite, quartz monzonite, monzodiorite and quartz monzodiorite whereas the Southern samples are monzogranite and granodiorite. The rocks are generally calc-alkaline to mildly alkaline transitional and metaluminous, and show a CAFEMIC trend. The Northern Zone intrusions form a post-collisional, A-type, alkaline monzonitic association and Southern Zone intrusions form a post-collisional, I-type, granodioritic calc-alkaline-transitional association. Whole-rock compositional data indicate that differentiation occurred via fractional crystallisation with or without magma mixing. Incompatible and rare earth element patterns indicate that both the Northern and the Southern Zone intrusions were derived from melting of a mantle region enriched by subduction-related fluids but evolved differently during ascent and emplacement. U–Pb zircon dating in the Southern Zone yields an intrusion age of 44.4±0.3 Ma. Regional geodynamics indicates post-collisional extensional tectonics in the region. Crustal involvement and the level of emplacement may have been important for magmatic evolution, especially for the Southern Zone intrusions, after the cessation of subduction and subsequent crustal thickening.

Deformation-driven differentiation of granitic magma: the Stepninsk pluton of the Uralides, Russia

The wide compositional spectrum of the Variscan batholiths of the Urals, a continuum from gabbros (or diorites) to leucogranites, was produced by crystal fractionation, but the physical mechanisms involved in formation of the bodies remains obscure. To test whether syn-magmatic deformation was essential to enhance the efficiency of the process, we studied the Main Series of Stepninsk, a pluton emplaced into an active crustal-scale strike-slip shear zone. The Main Series (>95 vol.% of total granitoids) is high-K calc-alkaline, comprises rocks with SiO 2 from 51 to 77 wt.%, and stands out because most major and many trace elements yield excellent linear or curvilinear correlations with silica. It includes deformed gabbrodiorites to monzogranites, and undeformed syenogranites to alaskites. Deformed and undeformed rocks are coeval (283±2 Ma). All rocks, irrespective of their silica content, have the same initial Sr and Nd isotope ratios ( 87Sr/ 86Sr 283 Ma=0.70488±0.000131; ε(Nd) 283 Ma=−0.79±0.49), and contain amphibole and biotite with the same compositions. Based on thermodynamic and trace-element fractionation simulations, we propose a model of deformation-driven filter-pressing differentiation consistent with these features. The Main Series is derived from a hydrous high-K granodioritic magma which intruded containing ∼0.3 of early-formed solids. These accumulated locally by flow differentiation to produce the gabbrodiorites. The crystallization continued until the fraction of solids was higher than ∼0.55, after which different magma batches were efficiently squeezed by differential stress coupled with the opening of tensile fractures in the shear zone. This process produced a range of residua and segregates, the composition of which depended on the fraction of early-formed solids, the fraction of solids present when squeezing occurred and, especially, the efficiency of melt segregation. The monzodiorites and quartz–monzodiorites represent efficiently squeezed residua, the granodiorites to monzogranites represent unfractionated or little fractionated magma batches, and the leucogranites represent melt segregates with a few entrained crystals of amphibole and biotite. We proposed that wide-spectrum fractionation of granite magmas mainly occurs when they crystallize under compressive regimes, and is caused by deformation-driven filter-pressing differentiation.

HYDROTHERMAL As Bi MINERALIZATION IN THE NAKDONG DEPOSITS, SOUTH KOREA: INSIGHT FROM FLUID INCLUSIONS AND STABLE ISOTOPES

At the Nakdong As–Bi deposits, South Korea, Cambro-Ordovician sedimentary sequences are cut by numerous dykes of quartz monzodiorite and porphyritic granite. In the deposit, stage I involves arsenic mineralization, chiefly associated with arsenopyrite, pyrite, sphalerite and chalcopyrite, whereas bismuth mineralization characterizes stage II, with the coprecipitation of pyrrhotite, chalcopyrite, galena, bismuth, bismuthinite, cosalite, matildite, schirmerite, Au–Ag alloy, and argentite. The mineralization was initiated with the introduction of heterogeneous fluids of high salinity, presumably owing to the prominence of Ca, Mg, Na and K. At stage II, fluid immiscibility, which led to bismuth mineralization, produced (halite ± sylvite)-bearing highsalinity fluids of 27.6 to 49.3 wt.% NaCl equivalents, as well as low-salinity vapor-rich fluids. The homogenization temperatures of mineralizing fluids decreased only slightly from stage I, 283–416°C, to stage II, 222–395°C. A decrease in 18 O as well as 13 C in going from calcite in fresh limestone ( 18 O in the range +17.5 to +22.4‰, 13 C in the range +2.3 to +4.4‰) to silicified limestone ( 18 O in the range +13.3 to +18.3‰, 13 C in the range –2.5 to +1.3‰) were promoted not only by Rayleigh volatilization, but also by fluid–rock interaction, with the influx of magmatic fluids into carbonate rocks during the mineralization process. The fluid–rock interaction contributed to the CO2 and CH4 components in type-III fluids and also to the Ca-enrichment in type-I fluid inclusions. The prevailing species of sulfur in the mineralizing fluids is estimated to have been H2S. The 34 SH2S values obtained from the sulfide minerals increased from stage I, +3.2 to +4.4‰, to stage II, +4.1 to +4.8‰, values typical of magmatic sulfur, and the temperatures of homogenization of fluid inclusions increased as well. The decrease of sulfur fugacities, from 10 –9.1 –10 –6.4 atm at stage I to 10 –15.7 –10 –9.2 atm at stage II, through sulfide precipitation and H2S loss, induced the destabilization of bisulfide complexes and characterized the change of mineral stabilities from arsenopyrite – pyrite – sphalerite to bismuthinite – native bismuth assemblages.

Magma Mingling/mixing vs. Magmatic Fractionation: Geneses of the Shirakawa Mo‐mineralized Granitoids, Central Japan

Abstract. Leucocratic biotite granites are main components in the Hatogaya pluton and the Hirase stock in the Shirakawa region of central Japan. Molybdenite‐quartz vein mineralizations are widespread in and around the Hatogaya pluton and the Hirase stock, in which the largest is vein swarm of the Hirase mine. Mafic enclaves occur abundantly with granitic to granodi‐oritic matrix in the northern part of the Hatogaya pluton, while they are rare in the Hirase granitic stock. The enclaves with generally round shape have mostly diabasic to fine plutonic textures under the microscope, and show interfingering and lobate contacts with the felsic matrix. The enclaves are quartz monzodiorite in composition containing SiO&gt;2 mostly around 60 %. They have felsic blebs, thus are considered a mingled magma of basaltic compositions originated in depth and a felsic magma generated from the Hida metamorphic‐plutonic complexes or their basement.The mingled magma further mixed with and reacted with the felsic magma with SiO2 70 %, and then formed granodiorite‐granite of the high Na group (Na2O higher than 4.25 %). Thus, compositional variation of the northern part of the Hatogaya pluton was caused by the magma mingling. The mingling happened to be deeper level produced homogeneous granodiorite of the Mihoro pluton. Biotite granite of the low Na group (less than 4.25 %) could have originated in a granitic magma generated also from the Hida metamorphic‐plutonic complexes or their basement. Most of the granites, occurring in the southern part of the Hatogaya pluton and Hirase stock, show high Rb/Sr ratio, strong Eu negative anomalies and flat REE patterns, and are thus considered as fractionated products of the SiO2 70 % original magma. The strong concentration of molybdenum in the Hirase stock can be explained by high degree of magmatic fractionation which produced MoS2‐rich residual melts, suitable fractures developed at the latest Cretaceous time, and preservation of the mineralized fractures at the present level of erosion.